Thermoelectric generator



April 3, 1928. 1,664,720

7 C. W. WOODRUFF THERMO ELECTRI C GENERATOR Filed Dec. '7, 1925 /vv/vTOR A 1 CHARLES w. WOODRUFF fiT TORNE).

Patented Apr. 3, 192a.

FFICE.

CHARLES W. WOODRUFF, 0F COLUMBUS, OHIO.

THERKOELECTRIC GENERATOR.

Application filed December 7, 1925. Serial No. 78,987.

My invention relates broadly to a device for transforming heat energymto electrical energy.

More specifically my invention relates to a device for transformingalternating current or combustion energy into heat and utilizing thisheat to generate direct'current energy to be used as the supply for.

the filament and plate currents in vacuum tube circuits, or in any othersituation where a stead source of direct current is required or use 111.

Further, my invention relates to a method of manufacturing an improvedelement of a thermo-electric cell of the type employing hot and coldjunctions of dissimilar metals.

An object of my invention is to produce an improved form ofthermo-electric generator or cell in which the transformation from heatenergy to electric energy is at very high efliciency.

Another object is to produce a thermoelectric cell having a high currentcapacity without employing an excessive temperature in the cell duringtransformation.

A further object of my invention is to produce an improved constructionof a thermo-electric cell which will permit a ready transfer of a largeamount of heat from the source of heat to the hot junction, but willminimize the amount of heat conducted or transferred from the hotjunction to the cold 'unction.

A urther object of my inventlon is to provide a method for theeconomical manufacture of thermo-electric couples for the generation ofa steady direct current.

My invention is illustrated in the accompanying drawing, in which.

Fig. 1 is a plan View looking down upon the assembled device in sectiontaken along the line X-X of Fig. 2.

Fig. 2 is an end view in section taken along line Z-Z of Fig. 1.

Fig. 3 is a side view in section taken along line YY of Fig. 1.

Fig. 4 shows how the elements of my improved cell are made in acontinuous strip by my improved method of manufacture.

Referring to the drawing, the cell comprises a thermo-pile consisting ofa series of metallic couples, each couple comprising alternate strips ofdissimilar metals joined at their ends in serial relation, and a heatingelement C, to heat alternate junctions, or the hot junctions A, of thepile. The cold junctions B are arranged as far as necessary away fromthe hot junctions and from the heating element. The heating element C'is shown in Fi 3 in the form of a resistance grid which is heated bycurrent suitable source over wires J. The heating element C and the hotjunctions A are suitably supported adjacent each other in a closed innercontainer D, made of any suitable heat resisting material. Container Dis in turn enclosed within a compartment F of the main container, andthe space between D and F is filled with a suitable heat insulating andheat resisting material G. The elements of the thermo-plle are suitablysupported in insulated slots H-H formed in side walls of container 1)and compartment F. The cold junctions B extend into compartmentlE of themain container. The construction described above revents the loss ofheat by radiation, con ning ractically all the heat to container D, were it serves to heat the hot junction A, and it also prevents thetemperature of cold junctions B from being raised by heat from theheating elements C; The hot junction A may be heated by a gas flame orother suitable source of heat.

Compartment E is perforated with holes K to provide a free circulationof air around the cold junctions in order that the difference intemperature between the'hot and the cold junctions will be maintained asgreat as possible.

Each strip of dissimilar metal comprising the metallic couples is madein the form of a T, as shown in Fig. 2. Two of these strips ofdissimilar metals are joined togetherat their upper ends, across theentire cross-portion of the T, to form a hot junction of one couple. Thelower end of each strip is connected to the lower end of a strip ofdissimilar metal of an adjacent couple to form a cold junction. Thevertical portion of each strip is made as small as possible in order toreduce to a minimum the amount of heat conducted from the hot junctionto the cold junction. The size of this vertical portion is dependentsomewhat upon the amount of current which must be conducted over itwithout the generation of too much heat due to resistance. It is to benoted that by forming these elements in the form of a T as shown, thehot junction will have a comparatively large efiective area which can befrom any conveniently exposed to the heating element and will,accordingly, absorb a relatively large amount of heat, with the resultthat the current output of the cell will be many times that in case thehot junctions were mere point contacts.

By forming the couples with T shaped elements with the hot junction atthe top, the contact area of the hot junction is increased many timesover the case of contact between the ends of Straight wires, and theelectrical resistance of the hot junction is accordingly decreased. Thisresults in a lower internal resistance and, therefore, a more eflicientgenerator. p I

Due to the efiicient transfer of heat to the large area of the hotjunctions it islpossible to obtain a large current output' 'withoutmaintaining a high temperature within the container D.

The T shaped strips of the thermo-pile may be made of any of the wellknown dissimilar metals used in the construction of thermo-piles, andtheir ends may be joined together in anydesired manner, such as by acontinuous or solid weld across the entire top portion of the T, by spotwelding at spaced points along the top of the T, by crimping the two topportions together, or by depositing one metal upon the other.

The feature of my invention just described, that is, the feature offormingthe elements in the shape of a T, is not limited to, nordependent upon, the use of any particular materials nor any particularmanner of joining them together.

While the metallic couples may be made of two separate T shaped stripsof dissimilar metals joined together in the manner described above, theymay also be formed in a continuous strip in a manner now to bedescribed. I take a thin strip of metal of a Width equal to the lengthof the top portion of the T and of a length equal to the combined lengthof all the elements constituting the pile, and I- cut out portions ofthis strip to form the shape indicated in Fig. 4..

The central portion, running the whole length of the strip, is verynarrow, and constitutes the vertical portions of all the T elements. Thecross-portions are of a width equal to twice the width of thecross-portion of a T element, and these cross-portions are to constitutethe joined cross-portions of adjacent T elements of unlike metals. I

' next treat this strip in a manner to convert different and adjacentportions into metals of dissimilar properties. For example, the portionsindicated at L by horizontally ruled lines will constitute all the Telements of the strip corresponding to one dissimilar metal, and theportions mdicated at M by vertically ruled lines will constitute all theT. elements of' the strip corresponding to nom nee an alloy of thatmetal, I make the strip of the pure metal; 'and,'1n case the dissimilarmetals are to be two different alloys, I make the strip of a metal whichis a common constituent of the two alloys. Assuming that the dissimilarelements are, to be a pure metal and an allo of that metal, take, for

- example, the combination of the metal nickel (Ni) and anickel-chromium alloy (90 Ni-10 Cr). In this case the strip will beformed of nickel, which is the metal of one of the elements, say L.- Theother element M, which is to be an alloy, is formed from the nickelstrip in the following manner: The L portions are covered on all sideswith parafiin or any other suitable material, leaving the M portionsclean and exposed. Chromium is then deposited upon the surfaces ofportions M in suflicient quantity to combine with the nickel and formthe desired alloy. The chromium may be deposited upon the nickel by anysuitable rocess, for example, by electro-plating. .Kfter depositing thechromium, the paraffin is removed, and the entire strip is placed in asuitable furnace or oven and heated to a proper temperature to causecomplete diffusion of the nickel and chromium, thereby converting theportions M into an alloy of nickel'and chromium. The strip is nextfolded along the junction lines A and B in such manner that all the hotjunctions A are on one side of the pile and the cold junctions B on theother side, as shown in Fig. 1. to be mounted-in its container. It isapparent that both portions L and M may be treated in the mannerdescribed above to form two different alloys, the strip being made of ametal which is common to both alloys. 4

In the foregoing description I use the term pure metal to distinguishfrom an alloy, not literally pure.

It is obvious that a metallic pile construct- The pile is now finishedand ready ed in accordance with the foregoing process i has manyadvantages: It is rugged and strong; the problem of making good contactbetween the dissimilar metalsis not present; it has low internalresistance, and has other advantages in addition to the advantages de- 7rived by formingthe elements in a T shape. M improved method ofmanufacturing -ent 5 ant volta purposes. Also, due to the compactness ofguano metallic couples'is not limited in its application to themanufacture'of elements 0 the T shape, but it is apparent that it may beapplied in the manufacture of elements of an shape or form,

nder any given conditions each couple of the generator will generate adefinite volta e, and by connecting a suflicient number 0 couples mseries, any desired voltage can be obtained at theterminals. In Fig. 1,I have shown'a series of terminals 1,, I, and 1,, which are tap d ontothe pile at differints to in'c ude different numbers of coup es, andwill, accordingly, have differacross the terminals As will be seen; isthe low voltage ta I the mtermediate and I, the high vo tage terminalsincluding the whole pile. Any desired number of taps may be provided.

Due to the inherent high current capac1ty, of my im roved generator itis articularly well. suited for use as a supply or the filament currentsof vacuum tubes in any use, whether for receiving, transmitting, orother my generator, it is easily possible to obtain fairly high voltagesand accordingly it is well suited for use as a supply for the platecurrent of vacuum tubes in any use, whether for the small currentrequired in receiving sets or for the large currents required in powertubes in transmitting sets.

'It is possible to arrange the terminals of a single generator so thatit will supply all the current needed by the usual receiving set.Forexample, the tap on the low voltage terminals may be ad usted to theproper voltage to supply the filament current, the intermediate voltageterminals adthe details of construction, and the materials justed tosupply the detector plate current and the high voltage terminals tosupply the amplifier plate current. Since the heatlng element C may beheated from any suitable source of current or. heat, it may be designedto operate from the ordinary house-lighting system, and the generatormay be made 1nto a convenient form and sold as a battery eliminator orbattery substitute for use in radio sets or ignition systems, or forlighting, etc. i

While Ihave described certain details of construction, and named certains ecific metals in the foregoing description, it was by way ofexplanation of the invention and not by way of limitation. It is obviousthat used, may be varied throughout wide limits without departing fromthe spirit of my invention. 7

I claim:

1. Elements of a thermo-electric generator comp-rising a homogeneousstrip of base metal-having different metals diffused therethrough indifi'erent portions thereof, said strip being relatively Wide atalternate junctions of unlike portions and having narrow sectionsmtermediate the wide junctions. v 2. Elements of a thermo-electricgenerator comprising a homogeneous strip'of base metal having differentmetals diffused there through in different portions thereof, said stripeing relativel wide at alternate junctions of'unlike portions and havingnarrow sections intermediate the wide unctions, said wide junctionsconstituting the hot junctions of said generator.

, 3. Elements of 'a thermo-electric generator com rism a-homogeneousstrip of base materia having different metals difiused therethrough indifferent linear ortions thereof, alternate junctions of unlike portionsconstitutin hot junctions of the generator, the remaining unctionsconstituting the cold junctions, sa1 strip having reducedcross-sectional area intermediate the hot and cold 'unctions toreduce-the transmission of heat etween said junctions.

1 4. A thermo-pile comprising a series of aligned hot junctions forminga heat receivmg surface, a series of aligned cold junctions, and aportion connecting said hot and cold junctions having cross sectionalarea smaller than the heat receiving surface, said thermo 'through inalternate portions thereof.

7. Elements of a thermo-electric generator comprising a homogeneousstrip of base metal having diii'erent metals diffused there through indifferent portions thereof, said portions constituting respectively theposi- 8. Elements of a thermo-electric generator comprising a.homogeneous strip of base metal having an unlike metal diffusedtherethrough in alternate portions thereof, and a second unlike metaldiifused therethrough in adjacent alternate portions.

9. The method of making a generating element of a thermo-electricgenerator which consists informing the element of a metal and difi'usinga dliferent metal throughout a portion of the element.

10. The'method of making a generating element of a thermo-electricgenerator which consists in forming both positive and negative portionsof the element of a continuous piece of base metal and diffusing ametalthroughout one of the portions thereof.

11. The method of making an element of a thermo-electric generator whichconsists in tive and negative elements of the generator.

forming the element of a base metal into the desired shape and diffusingtherethrough a diflerent metal.

12. The method of making an element of a thermo-electric generator whichconsists in forming the element into the desired shape from a basemetal, depositing upon the element a different metal and heatlng theelement to cause diffusion of the metals.

13. The method of making the generating unit of a thermo-electricgenerator which consists in forming the elements of the unit in theiormof a continuous stripwof metal,

depositing a different metal on alternate portions of the strip andheating the strip to cause diffusion of the metals.

14.- The method of making the generating unit of a thermo-electricgenerator which consists in forming the unit in a continuous strip ofmetal, depositing a difierentmetal upon alternate portions thereof,heating the strip to cause diffusion of the metals, depositing a seconddifferent metal upon the remaining portions of the strip, and heatingthe strip to cause diffusing of the metals.

= 15. The method of making the generatin unit of a thermo-electricgenerator which consists in forming the elements of the unit in the formof a continuous strip of metal, depositing a different metal onalternate portions of the strip, heating the strip to cause diffusion ofthe metals, and forming the strip into an accordion-like pile with thehot junctions on one side and the cold junctions on another side.

16. The method of making the generating unit of a thermo-electricgenerator which consists in forming the unit in a continuous strip ofmetal, depositing a different metal upon alternate portions thereof,heating the stri to cause diffusion of the metals, depositing a seconddifl'erent metal upon the remainmg portions of the strip, heating thestrip to cause difi'using of the metals, and forming the strip into anaccordion-like pile with the hot junctions on one side and the coldjunctions on another side.

In witness whereof I afiix my signature.

CHARLES W. WOODRUFF.

